1. Field of the Invention
This invention relates to a cylinder device, and more specifically to a variable force cylinder device in which a pressure-receiving area of a piston is altered depending on the travel distance of the piston in a cylinder chamber so that the force yielded by the piston is varied.
2. Description of the Related Art
A clamping device having a crank mechanism coupled to a cylinder device has been used to hold a workpiece.
In the cylinder device incorporated into such a clamping device, a piston is moved by a pressurized fluid introduced into a cylinder chamber and the reciprocating motion of the piston is transferred to the crank shaft to cause the crank arm to rotate. Conventionally, the force produced by the piston is constant regardless of the phases in a piston stroke, or the travel distance of the piston in the cylinder chamber. Therefore, the force for clamping the workpiece exerted by the crank arm is also kept constant regardless of the travel distance of the crank arm. Hence, there has been a danger of injury in which an operator has his/her hand or fingers pinched by the crank arm.